Scanning for answers

Imaging, in its various flavours, has become a vital part of medical diagnosis and it's no surprise that the 1979 Nobel Prize was awarded to the American Allen Cormack and EMI's Godfrey Hounsfield for their independent development of xray computed tomography, or CT scanning. In the 1960s, Hounsfield developed an idea of determining what was inside a box by taking xray readings at all angles around that box. He then developed a computer that could take input from xrays to build an image of an object using slices. He built a prototype scanner, testing it first on a preserved human brain, then on a fresh cow's brain. Finally, he tested it on himself. CT scanning was first used in 1971, where a patient with a cerebral cyst was scanned at Atkinson Morley Hospital in London. Hounsfield then developed a full body scanner, which EMI introduced in 1975. Since then, the technology has developed in a number of ways. Amongst the scanning techniques currently in use are: radiography; magnetic resonance imaging (MRI); nuclear medicine; photoacoustic imaging; tomography; and ultrasound. Of these, perhaps MRI and ultrasound are the more widely recognised. MRI – for which Sir Peter Mansfield and Paul Lauterbur won the 2003 Nobel Prize – works on the principle that the body is mostly composed of water. In particular, it uses the fact that water molecules contain two protons. When these enter a magnetic field, they align in its direction. An rf field is then applied, the protons absorb energy, releasing it when the field is turned off. Because protons in different types of tissue return to their equilibrium states at different rates, an image can be created. Ultrasound is based on the emission of a high frequency signal and detecting the reflections. Depending on the time taken for the echo to return and its strength, the system can create an image of the field of view. Medical scanners are generally large and capital intensive. And it is only recently that the relatively low cost ultrasound technique has appeared in the field. So it's no surprise that demand is increasing for wider access to scanners. Craig Buckley, regional service manager for Siemens Healthcare, said there were two main drivers for scanning technology. "They're not exactly opposed," he noted, "but they are at opposite ends of the spectrum. The clinical market, where systems are used for diagnosis, is the biggest area. Cost pressure here is coming from the NHS and the private sector. Meanwhile, demand for MR – or non ionising – systems is being driven by users wanting more for less; they're looking for more resolution and better flexibility." Buckley pointed out that MR technology can be improved by addressing a number of areas. "There's the rf chain, for example, where we can combine multiple coils. Then there are things like work flow." Work flow is an important element – it's the medical equivalent of productivity. "If you're taking multiple body images," Buckley observed, "the patient has to be repositioned and that could take 30 minutes a time." Moving from a head coil to a neck coil, then imaging extremities takes time. "And time is money, so there is a need to cut imaging time, not only from the technical perspective, but also from the work flow aspect." The latter is being addressed by adding intelligence in the table moving system. But Buckley highlighted a serious constraint. "MR is only effective within a spherical volume of 40 or 50cm diameter. The body has be in the centre of this volume because that's where the lines of flux are parallel." It's not only a problem when it comes to positioning the patient, it can also be a problem getting the patient into the scanner. As Buckley noted: "People are getting larger." Stronger magnets are one way in which to get a larger bore. Today, most scanners work with a field strength of 1.5Tesla, but 3T systems are beginning to appear. However, magnets need to be bigger in 3T systems. According to Buckley: "If you increase field strength, you have to make the bore longer. This means more coil windings, more energy and more cost. Siemens has made a number of improvements that allow the magnets to be shortened, but the field strength maintained and the bore widened. But there are a lot of physics challenges." Medical researchers, however, want more power. "We are just about to take an order for a 7T machine," Buckley claimed, adding that 7T imaging is in the same position as 3T was a decade ago. "There's a lot of development work involved in trying to combine the rf electronics with the magnets, but 7T does bring better resolution images." More interestingly, Siemens is working to combine two imaging technologies – MR and positron emission tomography, or PET. Such a device would acquire MR and PET scans at the same time and allow a high degree of registration. "Data acquired by both systems can be overlaid," Buckley noted, "providing an image of the body part and how it is reacting. Although this approach will have wide application in the future, the challenge today is getting the necessary technology into the magnets." And it's things like this which are focusing the attention of GE Healthcare. Alan Davies, chief medical officer for the company's EMEA operations, said: "We're focusing on structure and function. It's what the structure does that's important. For example, a heart can demonstrate narrowing of the coronary artery by imaging, but we also need to know what that image means. Does that narrowing impact heart function?